Question

问题在于while循环内的if语句。它没有打印所需的输出。 else if语句和else语句似乎正常工作感谢您的帮助

#include <iostream>
using namespace std;
/*
  Write a C++ program that asks the user for an integer. 
  The program finds and displays the first power of 3 
  larger than the input number using while 

*/
int main() {
  int input = 0;
  int base = 3;
  int exponent = 0;
  int sum = 1;

  cout << "Enter a number: ";
  cin >> input;

  while (sum < input) {
    // This is the if statement giving me problems
    if (input == 1) {
      exponent += 1;
      sum = 3;
    }
    // This else if statement seems to work fine
    else if (input == 3) {
      exponent += 2;
      sum = 9;
    }
    else {
      exponent++;
      sum *= base;
    }
  }
  // Print output 
  cout << "3 to the power of " << exponent << " is equal to " << sum;
  cout << endl << "It is the first power of 3 larger than " << input;
  return 0;
}

Answer 1

您的逻辑是错误的（我不得不说有点奇怪）。

如果input为1，则while (sum < input)不正确，因此您永远不会到达if (input == 1)语句。

Answer 2

纠正了我的错误。我只是将if和else if语句移到了循环之外

#include <iostream>

using namespace std;
/*
  Write a C++ program that asks the user for an integer. 
  The program finds and displays the first power of 3 
  larger than the input number using while 

*/
int main() {
  int input = 0;
  int base = 3;
  int exponent = 0;
  int sum = 1;

  cout << "Enter a number: ";
  cin >> input;

      if (input == 1) {
      exponent += 1;
      sum = 3;
    }
    else if (input == 3) {
      exponent += 2;
      sum = 9;
    }
  while (sum < input) {

      exponent++;
      sum *= base;
  }

  cout << "3 to the power of " << exponent << " is equal to " << sum;
  cout << endl << "It is the first power of 3 larger than " << input;
  return 0;
}

Answer 3

如果我从评论中理解了客观权利，则不需要if条件。只需替换条件并简化while循环即可，如下所示：

  while (sum <= input) {
    exponent++;
    sum *= base;
  }

Answer 4

编写一个C ++程序，要求用户输入整数。该程序查找并显示比输入数字大3的第一幂使用while

您可能应该计算答案而不是循环。

#include <iostream>
#include <cmath>

int main() {
    int input;
    std::cout << "input: ";
    std::cin >> input;
    int x = 0;

    /*    
          3^x == input
      ln(3^x) == ln(input)
      x*ln(3) == ln(input)
            x == ln(input)/ln(3)
    */

    // calculate x = ln(input)/ln(3),  round down and add 1
    if(input > 0) x = std::floor(std::log(input) / std::log(3.)) + 1.;

    std::cout << "answer: 3^" << x << " == " << std::pow(3, x) << "\n";
}

C ++ if语句未打印所需的输出

4 个答案: